The present invention relates to a covering sheet which can give matt feeling and, furthermore, preferred soft touch feeling, to a portion where people may touch, e.g., interior of automobiles, architectural interiors, housings of office automation equipment, household electrical goods, etc., stationery, sanitary goods, and is daily necessities; and to a method of producing the sheet and a molding using the sheet.
In order to provide surfaces of plastic moldings or metallic moldings with matt feeling (for example, suede-like soothing external appearance), suede-like covering coats are formed using paints or a shoot for moldings obtained by using paints.
For example, a suede-like shoot for molding is proposed in Japanese Laid-Open Patent Publication No. 2-41243 which is obtained as follows. The matt point which includes a bead pigment and an ionizing radiation curable resin vehicle is coated onto a base film having good moldability and cured.
However, since it is necessary to cure the ionized radiation curable resin composition by irradiation with an electron beam, etc. after the application thereof on a film, production steps for the sheet become complicated and the productivity is not satisfactory. Moreover, since a coating film of the sheet is made of a resin which is crosslinked using an electron beam, etc., the extensibility of the entire sheet is poor.
Japanese Laid-Open Patent Publication No. 59-202830 proposes an apparatus in which a molding is decorated while being engaged in injection molding using the sheet.
When the sheet disclosed in above-mention Japanese Laid-Open Patent Publication No. 2-41243 and the apparatus proposed in Japanese Laid-Open Patent Publication No. 59-202830 area incorporated in an attempt to obtain a molding having a soft touch feeling on the surface, the following problem arises.
When attempts are made to adhere the sheet onto the surface of the molding having unevenness or curves, there is a risk of the sheet being cracked since the extensibility of the shoot in poor. In particular, it is difficult to easily give matt feeling and soft touch feeling to the molding in deep draw forming.
Furthermore, Japanese Laid-Open Patent Publication No. 62-251111 proposes a method of producing a molding, comprising the steps of: previously placing a thermoplastic resin sheet in a mold; introducing a resin in the mold; and pressing the resin in the mold with a cope, thereby obtaining a molding having the thermoplastic resin sheet (decorating sheet) adhered to the surface thereof.
However, the molding obtained by the method proposed in Japanese Lain-Open Patent Publication No. 62-251111 does not produce matt feeling since its surface layer is formed only of the thermoplastic resin and minute unevenness is not formed on the surface. Also, touch feeling is rather stiff. Therefore, this production method cannot be used to produce products which require matt feeling or soft touch feeling to the human skin, e.g. interior of automobiles, housings, cases, etc.
The present invention overcomes the above-mentioned problems, and has the features of providing a covering sheet which has matt condition on its exterior and, furthermore, which has a soft touch feeling; a method of producing the same with good productivity without creating problems associated with conventional painting space or environmental problems associated with using solvents; and a method of producing a molding using the covering sheet.
Another feature of the present invention is to provide a method which can produce the above-mentioned covering sheet at relatively low cost.
A covering sheet of the present invention is made of a composition containing urethane type thermoplastic elastomer and elastic fine particles as main components.
A surface layer having minute unevenness on the surface thereof, an adhesive layer, and a substrate layer comprising an olefin type thermoplastic elastomer are laminated in this order to form the covering sheet.
In a method of producing the covering sheet of the present invention, the composition containing the thermoplastic elastomer and the elastic fine particles as main components is extruded, and then expanded, thereby obtaining the covering sheet having minute unevenness on the surface.
Since the covering sheet obtained in the method of the present invention is formed of the composition containing the-thermoplastic elastomer and the elastic fine particles as main components, and since the covering sheet has the surface layer having minute unevenness on the surface; matt feeling on the appearance, and generally, soft touch feeling can be given to a surface of a molding.
According to the method of producing the covering sheet of the present invention, minute unevenness is formed on the surface by extruding the composition containing the thermoplastic elastomer and the elastic fine particles as main components into a sheet-like shape, and then by expanding it. Therefore, it is not necessary to use a solvent and the sheet can be produced in good working environment. Moreover, since the sheet may be produced in a co-extruding method in a case where the covering sheet has a substrate layer, it is possible to perform continuous production in a single stop unlike the case where a paint is applied after the production of the substrate layer. Minute unevenness refers to the presence of bumps or waviness on the surface.
Therefore, a covering sheet which has matt feeling on its appearance, and generally, a soft touch feeling can easily be produced with considerably good productivity without creating conventional problems associated with a paint space or an environmental problem associated with using solvents, and the like.
Thermoplastic Elastomer
The thermoplastic elastomer for use in the present invention refers to a polymeric material which exhibits what is called rubber elasticity at room temperature and is capable of being plasticized into a variety of moldings at high temperature.
Examples of the above-mentioned thermoplastic elastomer include polyurethane type, polystyrene type, polyolefin type, polyester type, polyvinyl chloride type, polyamide type, ionomer type, fluororubber, 1,2-polybutadiene type, trans 1,4-polyisoprene type, synthetic natural rubber type, etc., which can be used either alone or in combination.
It is often the case that thermoplastic elastomer generally includes within a molecule both a rubber component (soft segment) having entropy elasticity and a molecular binding component (hard segment) preventing plastic deformation, and it sometimes includes a partial crosslinkage structure in a moldable range. However, it does not include an extensive, 3-dimensional network crosslinkage structure.
Hardness of the thermoplastic elastomer is preferably in the range of 20 to 98 in A hardness of JIS K6301, although it differs depending on the degree of touch feeling desired and the hardness of elastic fine particles (elastic beads are often used) to be used.
Specific examples of the above-mentioned thermoplastic elastomer of polyurethane type include block copolymer having polyurethane as hard segment, and polyether, polyester, polycarbonate, etc. as soft segmnent.
Specific examples of polystyrene type include block copolymer which has polystyrene as hard segment, and which has polybutadiene, polyisoprene, polyethylene-polybutylene as soft segment (referred to as SBS, SIS, SEBS block copolymers, respectively); and a block copolymer in which said block copolymer is further hydrogenated or supplemented with additional functional groups.
Specific examples of polyolefin type include
those which have polyolefin such as polypropylene as a hard segment, and which have ethylene as a soft segment (referred to as EPM (ethylene-propylene-methylene bonding)); those which have a polyolefin such as polypropylene as a hard segment, and which have a small amount of diene component together with ethylene as a soft segment (referred to as EPDM (ethylene-propylene-dienemethylene bonding), EPM and EPDM together being called EPR (ethylene-propylene rubber)); those which are obtained by blending the above; those which are partially crosslinked by further adding an organic peroxide; those which are graft-modified with a derivative of an unsaturated hydroxy monomer or unsaturated carboxylic acid; butyl rubber graft polyethylene, etc. The hard segment and the soft segment can be blended either after the preparation of each as described above or during polymerization.
Specific examples of polyester type include copolymers which have polyester as a hard segment and polyether as a soft segment, etc.
Examples of polyvinyl chloride type include those obtained by a method where degree of polymerization of polyvinyl chloride is raised to the extreme (polyvinyl chloride of high degree of straight chain polymerization; degree of polymerization being in the range of about 2000 to about 2500), a method where a 3-dimensional crosslinkage structure is introduced to a part of polyvinyl chloride, a method where an ion crosslinkage structure is introduced to a part of polyvinyl chloride, etc.
Examples of polyamide type include those which include polyamide as hard segment and polyether as soft segment.
Selection of a specific thermoplastic elastomer is made by considering the particular performance characteristics of a covering sheet to be obtained. For example, if scratch resistance, abrasion resistance, and excellent touch feel and appearance are desired, thermoplastic elastomers of the urethane type are preferably used. As the urethane type elastomer, if light resistance and heat resistance are desired for a covering sheet, non-yellowing type using an aliphatic isocyanate, etc. is preferably used.
Elastic Fine Particles
Elastic fine particles which do not melt under extruding conditions for the above-mentioned thermoplastic elastomer, i.e., elastic fine particles having a softening temperature higher than the extruding temperature of the thermoplastic elastomer are used. The reason is as follows. If elastic fine particles are melted to become integrated with the thermoplastic elastomer when they are mixed in the thermoplastic elastomer and extruded from an extruder, then even if the sheet is expanded later, it becomes difficult to form unevenness of a desired size and shape on the sheet surface.
An elastic fine particle used in the present invention is a fine particle having the property that it elastically recovers when pressure is applied until the shape deforms and then is released. For example, an elastic bead having a diameter of 50 xcexcm which requires a weight of 0.5 to 30 gf in order to be pressed to a height of 40 xcexcm on a plane of a truncated cone is preferable. Particularly, those requiring 0.5 to 10 gf are preferable.
Usually, a non-natural elastic fine particle is used. Examples include those made of polyurethane, an acrylic resin (preferably an acrylic-urethane resin), polystyrene, styrene-isoprene copolymer, etc.
Although these elastic fine particles preferably have a spherical shape, those which are obtained by a method such as freeze crush and have a non-spherical shape can also be used.
A mean particle diameter of the elastic fine particle is usually in the range of 1 to 50 xcexcm, preferably in the range of 5 to 40 xcexcm, but generally 20 to 200 parts by weight, or preferably 50 to 150 parts by weight thereof are added to 100 parts by weight of the above-mentioned thermoplastic elastomer.
If the mean particle diameter of the elastic fine particle falls below 1 xcexcm, it becomes difficult to obtain a covering sheet having sufficient soft touch feeling (somewhat of a dampish touch feeling when touched). If the diameter further becomes extremely small, matt feeling cannot be produced. On the other hand, if the moan diameter of the elastic fine particle exceeds 50 xcexcm, it becomes likely that a crack may appear on a surface of a covering sheet when it in spread and drawn. Also, if an addition amount with respect to 100 parts by weight of the thermoplastic elastomer is less than 20 parts by weight, it becomes difficult to form minute unevenness on the surface of the covering sheet and, consequently, matt feeling or soft touch feeling of the covering shoot decreases. It the addition amount in more than 200 parts by weight, a crack may be easily formed on the surface of the covering shoot when it is spread and drawn.
Also, the kinds of elastic fine particles are not limited to one, but instead, two or more kinds of elastic fine particles can be used in combination. When a relatively flexible thermoplastic elastomer is used, or when a slight stiffness on the surface of the covering sheet is acceptable, crosslinked polymethyl methacrylate or hard fine particles made of inorganic materials can be used with the above-mentioned elastic fine particles.
Covering Sheet
A construction of a xe2x80x9ccovering sheetxe2x80x9d of the present invention is as follows.
(1) For example, a sheet having a surface layer, an adhesive layer, and a substrate layer laminated in this order is described as follows.
The surface layer is made of a composition containing a urethane type thermoplastic elastomer and elastic fins particles as main components, and as a result has minute unevenness on the surface thereof.
The substrate layer is made of an olefin type thermoplastic elastomer. The adhesive layer for the two layers mentioned above is preferably a layer made of a polyolefin (particularly polypropylene) modified by an acid such as unsaturated polybasic acid or of SEBS (styrene-ethylene-butylene-styrene copolymer) further modified by an acid such as unsaturated polybasic acid, although this does not particularly limit the choice.
Since the construction is such that the surface layer and the substrate layer are laminated with the adhesive layer interposed therebetween, an amount of the elastic fine particles to be used can be reduced by dispersing the particles only in the Surface layer of the covering sheet compared to the case where the elastic fine particles are dispersed in an entire laminated layer. Also, in a case where a melted resin and the covering sheet are integrated during production of, for example, a molding by injection molding or injection press molding, the adhesiveness of the two layers can be made excellent by having the substrate layer made of the same molding resin.
A detailed construction of each layer, including minute unevenness of the surface layer, is to be described in the section xe2x80x9cmethod of producing the covering sheetxe2x80x9d in the specification.
(2) A sheet having a surface layer, an adhesive layer, a substrate layer, and a foamed resin layer laminated in this order is described as follows.
A construction of the surface layer, the adhesive layer, and the substrate is the same as in the case (1) above. Examples of the foamed resin layer include foamed layers made of a polyolefin type resin, a polystyrene type resin, a polyurethane type resin, a polyvinyl chloride type resin, a variety of thermoplastic elastomer resins, etc. In particular, the use of a foamed layer made of the polyolefin type resin is preferable in that it has excellent adhesiveness to an olefin type thermoplastic elastomer substrate layer, has an excellent cushioning properties, and enhances soft touch feeling of the surface layer when pressed.
Method of Producing the Covering Sheet
The xe2x80x9cmethod of producing the covering sheetxe2x80x9d will be described below.
(1) Production of the covering sheet made of a single layer is described as follows.
The covering sheet is obtained by melt-kneading a composition containing a thermoplastic elastomer, elastic fine particles and, if necessary, an additive, extruding it in a sheet-like shape using a kneading extruder such as a biaxial extruder, and then expanding the sheet in the longitudinal direction, and optionally, in the width direction.
Known conditions for extruding a thermoplastic elastomer may be generally employed as conditions for the above-mentioned extruding, although they depend on the identity and mixing ratio of the thermoplastic elastomer, the elastic fine particles, and the additive. For example, it is possible to perform extrusion in a temperature range of 150 to 215xc2x0 C. when thermoplastic urethane elastomer is used as the thermoplastic elastomer.
Instead of mixing the thermoplastic elastomer, the elastic fine particles, and the additive, and then melt kneading and extruding the composition by the biaxial extruder, a uniaxial extruder may be used if the above-mentioned components are mixed by a Banbury mixer and pelletized by a pelletizer, etc.
An expansion of the above-mentioned sheet-like body can be conducted in half-solid state immediately after extrusion if the sheet-like shape is maintained. Certainly, it can also be conducted in solid state (generally referred to as drawing in this case). Specifically, the above-mentioned composition in the sheet-like shape immediately after extrusion (discharge) from the extruder can be expanded by pulling rollers, etc. Alternatively, It can be expanded after cooling and forming the composition in the sheet-like shape enough to be rolled. Furthermore, the extruder (metal mold) can be arranged in such a manner that the composition of the sheet-like shape be extruded vertically down and the sheet be expanded by its own weight.
The drawing of the sheet is usually performed as follows. The temperature of the sheet is lowered below the softening temperature of the thermoplastic elastomer used. The sheet makes contact with cooled rollers, and is received by pulling rollers which are provided on the extruding side of said cooled roller and are rotating with speed faster then the extrusion speed of the sheet. If pulling rollers, such as cooled rubber rollers whose surface is processed for roughness, are used, the sheet can be expanded by these rollers in the vicinity of the softening temperature of the thermoplastic elastomer. Tenter expanding method can also be employed.
A term xe2x80x9csheet-like bodyxe2x80x9d in the present invention includes both a half solid state immediately after the extrusion and a solid state after sufficient cooling (so does a sheet-like shape laminated member to be described in section (2) and beyond).
The expendability of the sheet is usually 1.2 or greater, preferably in the range of 2 to 50, or more preferably in the range of 2 to 20 although it varies depending on the miscibility of the elastic fine particles and the thermoplastic elastomer to be used, the hardness of the elastic fine particles, and the softening temperature of the thermoplastic elastomer.
The expandability K of the sheet is given by the formula below:
K=(area of cross-section of metal mold lip)/(area of cross-section of the received sheet).
As described above, by expanding the sheet, a sheet having minute unevenness on the surface attributable to the elastic fine particles is obtained. Since light is scattered by the minute unevenness, the covering sheet obtained produces matt feeling when viewed and soft touch feeling (suede-like feeling) when touched.
The reason why minute unevenness is formed on the surface of the covering sheet is conjectured as follows.
As shown in FIG. 1, when the sheet 40 extruded from the extruder is expanded, the layer 44 made of the thermoplastic elastomer is stretched in the direction of expansion of the sheet 40 and a thickness of the thermoplastic elastomer layer 44 gradually becomes small while the elastic fine particles 41 contained in the sheet 40 hardly deform. As a result, portions of the thermoplastic elastomer layer 44 surrounding the elastic fine particles 41 become thin, thereby forming convexs 43 on the sheet surface 42.
Preferably, configuration of the unevenness formed on the covering sheet is as follows.
As described above, the minute unevenness on the surface of the covering sheet is produced by the added elastic fine particles disposed on the surface thereof. The convex is formed by one or a congregation of a plurality of the added elastic fine particles.
As shown in FIG. 2, the width of the convex 29 is preferably in the range of 1 to 50 xcexcm on average, or more preferably in the range of 4 to 30 xcexcm on average although it may change depending on the size of the added elastic fine particle. The reason for this is as follows. if the width W of the convex 29 is too small, then it becomes difficult to obtain matt feeling or excellent touch feeling. On the other hand, if the width W is too large, then a crack easily appears on the surface when the covering shoot is being spread, although it depends on the precise thickness of the covering sheet. Touch feeling also becomes poor and matt finish becomes unsatisfactory.
A width of the convex 29 is defined to be a length between the lowermost points on both sides of the convex 29 as indicated in FIG. 2.
A density of the unevenness is preferably 10 particles per 0.01 mm2 or greater, or more preferably 15 to 100 particles per 0.01 mm2, although it may vary depending on the size of the added elastic fine particles. It is also preferable that the unevenness is formed continuously. If the density of the unevenness is less than that in the above-described ranges, then matt feeling becomes unsatisfactory.
The matt feeling of the covering sheet can be measured, for example, in terms of specular glossiness. In that case, the glass value measured in conformity with JIS K7105 is preferably 5 or less, and more preferably 3 or less, in terms of 60xc2x0 specular gloss.
Roughness of the covering shoot is preferably in the range such that Rzxc2x7D=5 to 50 xcexcm, or more preferably Rzxc2x7D=5 to 35 xcexcm in terms of ten-point mean roughness measuring a length of 4 mm with cut-off value being equal to 0.8 mm.
Here, the cut-off value refers to a wavelength for which the gain becomes 75% when a high frequency filter having an attenuation rate of xe2x88x9212 dB/oct is used in finding a roughness curve.
The ten-point mean roughness Rzxc2x7D is a value obtained as follows. A portion of the measuring length L is taken out from the roughness curve in the direction of the center line. The measured length is then cut into five parts of equal length, and the maximum heights (Z) in each of the equally partitioned intervals are averaged. It is expressed by the following equation.
Rzxc2x7D=(⅕)(Z1+Z2+Z3+Z4+Z5)
The surface of the covering sheet can further be given unevenness or a pattern by embossing, etc. in addition to the unevenness formed mainly by the elastic fine particles.
The covering sheet obtained as above is annealed if necessary.
(2) Production of the covering sheet having a surface layer with minute unevenness on the surface thereof and a substrate layer laminated on one side of the surface layer is described as follows.
When a composition which contains a thermoplastic elastomer and elastic fine particles as main components and is to become the surface layer and a thermoplastic resin to become a substrate layer are laminated to produce a laminated member of a sheet-like shape by co-extruding them together, the two layer can easily be laminated without trapping air therebetween, and the sheet can easily be produced in a single step. Therefore, the above factors are particularly preferable in actual production.
When the obtained laminated member is expanded, even if the surface layer has such a thickness that it would be difficult to expand it if the surface layer consisted of the single surface layer, the surface layer can easily be expanded together with the substrate layer.
The co-extruding forming refers to a method of producing a product having a multilayer structure by combining resins extruded respectively by using two extruders or more.
The combining method of the co-extruded resins roughly includes the feedblock method, the multimanifold method, and the multislot die method.
In the feedblock method, the combining is done by a special block provided immediately before the die. The method is also called a black box method.
In the multimanifold method, the die includes a necessary number of manifolds for the layers.
In the multislot die method, the die includes separate flows and the adhesion takes place immediately after coming out of the die.
In any one of these methods, a sheet having a plurality of layers can be produced. A combination of these methods (for example, a combination of the feedblock method and the multimanifold method) is also possible.
The sheet can be formed as follows. The thermoplastic elastomer which constitutes the surface layer and the elastic fine particles are mixed. Then, they are melt-kneaded and extruded by using a biaxial type extruder to be co-extruded and molded with a resin which is to become the substrate layer extruded from another extruder. The sheet can also be formed as follows. The thermoplastic elastomer and the elastic fine particles are kneaded and pelletized in advance. The pellet is then extruded by a regular extruder to be co-extruded and molded with a resin which is to become the substrate layer extruded from another extruder.
When the thermoplastic elastomer and the elastic fine particles are kneaded and pelletized in advance, the mixing of the thermoplastic elastomer and the elastic fine particles can be done by Banbury mixer, etc.
An example of the temperature condition for the above-described extrusion is 150 to 215xc2x0 C. in a case where a composition for the surface layer using the thermoplastic elastomer is extruded.
Examples of materials constituting the above-mentioned substrate layer include the thermoplastic elastomer used for the above-mentioned surface layer; or a thermoplastic resin such as polystyrene, acrylic polymer, polycarbonate, polyvinyl chloride, polyethylene, polypropylene, ABS (acrylonitrile-butadiene-styrene copolymer), modified polyphenyleneoxide, polyphenylenesulfide, polyetherimide, polyetheretherketone, and ionomer.
When giving the covering sheet an enhanced cushion property and tender soft touch feeling when the surface layer is pressed, it is preferable that the substrate layer is made of a thermoplastic elastomer.
A temperature condition for extruding olefin type thermoplastic elastomer is generally 180 to 230xc2x0 C.
The substrate layer can be made either of a single layer or of a plurality of layers.
(3) Production of the covering sheet having a surface layer with minute unevenness on the surface, an adhesive layer, and a substrate layer laminated in this order is described as follows.
If the adhesiveness between the surface layer and the substrate layer is poor in the above-described section (2), it is preferable to provide an adhesive layer between the two layers.
In this case, the surface layer, the adhesive layer, and the substrate layer are co-extruded to form a laminated member of a sheet-like shape in such a manner that they are laminated in that order, and then expanded.
Examples of the adhesive layers include pressure-sensitive adhesive and solvent type adhesives of the rubber type, acrylic type, urethane type, and silicone type; a layer made of hot-melt adhesive of, for example, ethylene-vinylacetate copolymer (EVA) type, chlorinated polyolefin, or styrene-isoprene-styrene block copolymer (SIS) type; a layer made of an adhesive resin such as polyolefin modified by an acid such as unsaturated polybasic acid and acid-modified SEBS (styrene-ethylene-butylene-styrene copolymer). These are called primer layers when appropriate.
For example, an after cure type adhesive of microcapsule cure type can also be used. Examples of the after cure adhesive include uncrosslinked unsaturated polyester type adhesives and uncrosslinked acrylic adhesives.
In a case where the surface layer made of thermoplastic elastomer of polyurethane type is laminated on the substrate layer made of a polyolefin type resin or elastomer, the adhesiveness can be improved by using those obtained by acid modification or graft modification of the material constituting the substrate, by blending these materials with unmodified polyolefin, or by laminating modified polyolefin substrate layer on the substrate sheet made of unmodified polyolefin.
(4) Production of the covering shoot having a surface layer with minute unevenness on the surface, an adhesive layer, a substrate layer, a foamed resin layer laminated in this order is described as follows.
This method is the same as the production method described in the above section (3) except that it further includes a lamination of the foamed resin layer on the substrate layer side after expanding the laminated member of a sheet-like shape.
In order to laminate the expanded laminated member of a sheet-like shape described above and the foamed resin layer together, a foamed resin sheet produced in advance is placed on the substrate layer side of the laminated member of a sheet-like shape which is being extruded and is in a melted condition, where they are passed between a pair of rollers thereby fusing and integrating for lamination (extrusion laminating method).
Depending on the situation, the foamed resin sheet can be extruded from another extruder immediately before the co-extruded laminated layer member of a sheet-like shape passes through the rollers thereby integrating them by pressing by the rollers.
Examples of a material for the above-mentioned foamed resin layer include polyolefin type resins (including those crosslinked) such as polypropylene and polyethylene; polystyrene type resins such as polystyrene and styrene-maleic anhydride copolymer; polyurethane type resins; polyvinyl chloride type resins; and various kinds of thermoplastic elastomer resins. Therefore, various kinds of foamed materials known in the art can be used. The expansion ratio of these foamed resin layer is usually in the range of about 5 to about 50, or preferably about 10 to about 50, or more preferably about 10 to about 40, in order to enhance the soft touch feeling when pressed.
The foamed resin layer can be of a single layer or of multiple layers. Furthermore, an adhesive layer may be laminated on the foamed resin layer in advance. In a case where the adhesiveness between the foamed resin layer and the core material (i.e., a molding body) onto which the foamed resin layer is laminated is poor, the adhesiveness between the two layers can be improved by providing an adhesive layer to the foamed resin layer in advance. Although the lamination of this adhesive layer can be done after the formation of the foamed resin layer, it is more efficient and preferable that the adhesive layer is laminated on an unexpanded green sheet constituting the foamed resin layer and then the green sheet in heated, thereby obtaining the foamed resin layer having the adhesive layer. A heat-sensitive adhesive can be used as an adhesive.
In order to improve design properties, a sheet provided with a pattern by printing, etc. can be laminated onto the above-mentioned substrate layer or foamed layer. (Covering sheet obtained by a xe2x80x9cmethod of producing the covering sheetxe2x80x9d of the present invention)
As described above, covering sheets having various kinds of layer structures such an a sheet made of a single surface layer; a covering sheet having a surface layer and a substrate layer laminated on one side of the surface layer either directly or via an adhesive layer; a covering sheet having a surface layer, an adhesive layer, a substrate layer, and a foamed resin layer, can be obtained in the production method of the present invention.
Any of the above sheets for covering has minute unevenness formed on the surface of the surface layer, giving excellent matt feeling and, usually, soft touch feeling.
Thicknesses of the layers constituting the covering sheet obtained in the method of the present invention are generally in the range of 5 to 500 xcexcm, or preferably 5 to 100 xcexcm, for the surface layer; in the range of 500 to 5000 xcexcm, or preferably about 1000 to about 3000 xcexcm, for the foamed layer; in the range of 100 to 3000 xcexcm, or preferably 200 to 1000 xcexcm, for the substrate layer; and in the range of 2 to 500 xcexcm, or preferably 5 to 50 xcexcm, for the adhesive layer (primer layer).
Furthermore, if necessary, materials, e.g., colorants such as a pigment and a dye, an antioxidant, a UV absorber, a UV stabilizer (e.g., hindered amine), and a flame retardant can be added to the covering sheet (at least any one of the surface layer, the foamed layer, and the substrate layer).
As the colorant, a pigment and a dye which are generally used in a paint can be used. Examples of the pigment include titanium oxide, iron oxide, carbon black, a cyanine type pigment, and a quinacridone type pigment. Examples of the dye include an azo type dye, an anthraquinone type dye, an indigoid type dye, and a stilbene type dye. Metallic powders such as an aluminum flake, a nickel powder, a gold powder, and a silver powder can also be used as the colorant. It is preferred that these materials have a particle diameter as small as possible.
The covering sheet (the surface layer in the case of multilayer structure) is formed of a composition having thermoplastic elastomer and elastic fine particles as main components (usually 50 weight % or greater in the composition).
The matt feeling and soft touch feeling produced by the elastic fine particle of the previously-set amount may decrease or become different if the solid colorant such as above-mentioned pigments and metallic powder is added to the composition. Therefore, if the composition contains the solid colorant, a mixing amount (usually in the range of 20 to 200 parts by weight) of the above-mentioned elastic fine particles for the thermoplastic elastomer (100 parts by weight) may be changed.
Furthermore, in order to give various kinds of properties to a covering sheet produced according to the present invention, materials for providing various kinds of properties can be added. Examples of the materials for providing various kinds of properties include a conductive material, an anti-fogging agent, a photochromic compound, etc.
Furthermore, in order to improve a design property of the sheet, patterning by printing, etc. may be conducted. In a case where the covering sheet is formed of a plurality of layers, it is preferable to provide the printing on the reverse side of the surface layer (e.g., on the substrate layer)
Use of a Covering Sheet
A xe2x80x9ccovering sheetxe2x80x9d or a covering sheet obtained by xe2x80x9ca method of producing a covering sheetxe2x80x9d can serve as various kinds of uses as described below.
In a method where a covering sheet is introduced in a mold and simultaneously adhered to a molding at the time of forming as for injection molding or injectionxe2x80x94press molding, the sheet is closely contacted with the inside of the mold at room temperature or by heating, using vacuum forming or pressure forming. After that, regular molding in conducted. In a case where the covering sheet is not largely spread or where the mold does not have corners of small curvature, the covering sheet may not have to be closely contacted with the inside of the mold in advance.
According to the method in which moldings are successively produced as in extrusion molding, pultrusion, etc., a covering sheet may be adhered to the surface of a molding at the same time that moldings are successively produced prior to sizing. Alternatively, after sizing or cooling the molding, the sheet may be adhered to the molding.
In a method of introducing the covering sheet into the mold, it is performed after taken out of the mold and before the cooling and sizing, or it is performed during the sizing so as to curl in the covering sheet. In a method where the covering sheet is attached immediately after the molding, the covering sheet is attached by pressing rollers in such a manner that the sheet goes along the outer surface of the molding.
In vacuum (pressure) molding, a covering sheet can be laminated on a molding shoot which becomes the core material in advance and then molded, or the covering shoot can be laminated on the core material during or after the molding.
In the case where the sheet is adhered to long members made of a material such an a wooden material or an aluminum sash, a commercially available profile laminator can be used. In this case, it is preferred that an adhesive layer in disposed on the covering shoot so as to make adhesion with respect to the member satisfactory.
A covering shoot on which a pressure-sensitive adhesive is disposed can be adhered to the surface of a molding by using hands, a double vacuum forming machine (machine for adhesion), etc.
As to the molding resin used in the above description, any materials which are usually molded can be used. Examples of these materials include ABS (acrylonitrile-butadiene-styrene copolymer), polyethylene, polypropylene, polyvinyl chloride, polystyrene, polycarbonate, acrylic resin, polyetherimide, polyphenylenesulfide, polyamide (nylon), thermosetting elastomer, etc. These materials mixed with a glass fiber or an inorganic filling agent are further included in the examples.
Method of Producing a Molding
Next, a xe2x80x9cmethod of producing a moldingxe2x80x9d of the present invention will be described more specifically.
A covering sheet used in this method is the covering sheet which is described in the sections 1 and 2 of xe2x80x9ccovering sheetxe2x80x9d.
Examples of method where a covering sheet and a molding resin are simultaneously molded together include the following.
(1) A covering sheet is introduced into a mold such that the surface layer thereof becomes the surface of the molding. Then, a molding resin for the molding is molded by injection molding or injection press molding while simultaneously attaching the covering sheet onto the front surface of the molding.
That is, the covering sheet is introduced into the mold such that the surf ace layer of the covering sheet is on the surface of the molding. Then, in a case of injection press molding, the mold is closed after introducing a molding resin into the mold to obtain the molding integrated with the covering sheet. In a case of injection molding, a molding resin is introduced into the mold after the mold is closed to obtain the molding integrated with the covering sheet.
(2) A covering sheet is pre-molded by pneumatic forming (vacuum forming and/or pressure forming) in advance. Then, this pre-molded sheet is introduced into a mold such that the surface layer thereof is on the surface of a molding to be obtained. Then, a molding resin for a molding is molded by in action molding or injection press molding while adhering the covering sheet onto the surface of the molding.
That is, in a case of stamping molding, the mold is closed after introducing the molding resin into the mold to obtain the molding. In a case of injection molding, a molding resin is introduced into the mold after the mold is closed.
In order to pre-mold the above-mentioned sheet, either (a) or (b) below can be performed. (a) The covering sheet is taken out from a mold for pre-molding, and introduced into a mold for a molding such that the surface layer side is on the front surface side. Then, the injection molding or injection press molding is performed to mold the main portion of a molding while integrating the pre-molded covering sheet on the surface of the main molding; or (b) the covering sheet is pre-molded in the mold for the molding, and the injection molding or injection press molding is performed to mold the main portion of a molding while integrating the pre-molded covering sheet on the surface of the main molding as in (a).
A molding can be obtained by molding a covering shoot without using a molding resin.
In that case, the covering sheet is introduced in the mold such that the surface layer thereof is on the front surface side of the molding, and the covering sheet is molded by vacuum forming or pressure forming such that the covering sheet is along the inner surface of the mold.
The pneumatic molding of the present invention refers to vacuum forming and/or pressure forming. Usually, plug assist molding known in the art, or a method where the sheet is once uniformly drawn by air pressure and then vacuum forming is performed can be used. Also, a mold used in the molding can be made of a resin instead of metal.